Recent theories of immunoregulation have suggested that idiotype recognition plays a key role in cellular interactions leading to antibody synthesis. The basic immunological unit of reactivity as defined by these considerations consists of an idiotype bearing B cell clone whose expansion, differentiation and expression of immunoglobulin synthesis is modulated by idiotypically restricted T helper, and T suppressive subpopulations. These reactions are likely to occur before the production of Id bearing anti-ARS antibody. The present proposal is designed to analyze the three idiotypically related cell populations that participate in the ARS-Id triad.